Hydraulic suspension unit

ABSTRACT

An improved hydraulic suspension unit has a springing force and rebound damping which are related to one another so as to allow certain wheel movements to occour without the resistance of rebound damping. A primary springing force provided by a pressurized gas, a coil spring and elastomer or any combination therof acts directly through the shock fluid via a floating piston, bladder or flexible diaphragm. The primary spring force acts directly through the shock fluid, and thus directly on a rebound damping valve so that the rebound damping valve is only able to dampen the stored energy. The spring provides a maximun in tuning and adjustment capability for varying conditions with easily variable reload and rate. The rebound damping valve can also be adjusted, both to determine the maximum rebound resistance when damping springing energy, and thus maximum shock shaft velocity, and to determine the magnitude of th shaft movements that are allowed to occur without rebound damping. Compression damping can also be adjusted independently of rebound damping, and provides very high flow rates, and a much more desirbale compression damping control. These adjustments can be made external to the suspension unit and require no disassembly. A lightweight vehicle is disclose which utlizes the improved hydraulic suspension unit.

FIELD OF THE INVENTION

The present invention is directed to an improved hydraulic suspensionunit for a vehicle and to a lightweight vehicle such as a bicycle ormotorcycle employing the same.

BACKGROUND AND SUMMARY OF THE INVENTION

There are many problems extant with current state of the art suspensionunits, whether they be for bicycles, motorcycles, four-wheel vehicles,on or off road. The shock designer must constantly weigh the relativeimportance of handling, control and ride comfort, and decide whichdirection to compromise the suspension performance toward the vehicle'sintended use. The only way to avoid these compromises would be to have asuspension that could anticipate every motion, and act to resist orcomply instantaneously. While many attempts have been made at developinga computer controlled suspension that will do just that, none are ableto achieve such a result. An object of the present invention is toreduce these compromises without requiring the use of a computer orelectrical components.

In the past, springing means and methods have been the first in line forcompromise during the process of specifying suspension components for agiven vehicle. Too stiff a spring rate prevents the suspension fromusing enough travel to cope with bumps or surface irregularities, andtransmits a harsh ride, as well as reduced cornering grip and tractionunder these conditions. Too soft a spring rate and the ride motionsbecome excessive and weight transfer induces large shifts in theattitude of the chassis during braking and cornering. Excessivebottoming can also occur. This compromise has been further complicatedin light vehicles such as motorcycles and bicycles, where rider weightis a relatively large percentage of the total sprung weight of thevehicle. For example, rider weight can be over 90% of total sprungweight in the case of a bicycle. With such a vehicle, a single springrate will not be well suited for all rider weights. The skill level ofthe rider or operator of the vehicle is also a consideration whenselecting a spring rate.

There is a need for an improved hydraulic suspension unit which providesa more flexible springing medium with more tuning capability, which canbe adjusted without resorting to physically changing components. Anobject of the present invention is to provide such a hydraulicsuspension unit.

Another compromise made with conventional shock absorbers is the amountof rebound damping. With conventional shock absorbers, there is always adamping effect present, even if this damping is undesirable. Too muchrebound damping can cause harshness in the ride as the suspension skipsoff the tops of bumps rather than allowing the wheel to follow thesurface into a depression. In a succession of bumps this can lead toloss of control as the wheel fails to return to full extension beforehitting the next bump, meaning less available travel to negotiate thenext bump, and more importantly, since the spring will be compressedwhenever the shock is not at full extension, it will provide a higherforce to resist the upward movement of the wheel upon hitting the nextbump. This problem is usually described as "packing down". Too littlerebound damping can cause an uncomfortable ride, by allowing too muchupward movement of the vehicle after hitting bumps, or due to weighttransfer in cornering, braking or accelerating. Too little rebounddamping can also allow excessive cycling of the suspension after theseinputs, as the spring's energy remains undamped, and is returned to thespring. Another problem is that too little rebound damping can cause thevehicle to launch skyward after large impacts, or when leaving the faceof a jump. This launching effect is caused when the suspension reachesfull compression, maximizing the stored energy in the spring, which isthen returned at a high velocity, due to inadequate rebound damping.

There is a need for an improved hydraulic suspension unit whichovercomes these drawbacks and disadvantages of the conventionalsuspension unit with respect to rebound damping. An object of thepresent invention is to provide an improved hydraulic suspension unitwhich solves these problems.

Compression damping is another area which has been compromised in theconstruction of conventional hydraulic suspension units. A vehicle withexcessive compression damping will feel very responsive to controlinputs, sometimes aiding handling by increasing control. This is usuallyat the expense of cornering grip or traction, as the wheel is unable toreact quickly enough to even minor surface imperfections, much lessbumps or major impacts and the contact pressure between the tire andterrain surface will be less consistent. When encountering a large bump,too much compression damping prevents the wheel from moving up over thebump quickly enough, thus translating impact to the chassis. Conversely,too little compression damping places too much reliance on the springingmeans for purposes of resisting excessive suspension compression due toweight transfer caused by cornering, braking, accelerating or bottomingforces. This can cause unwanted ride motions, as well as hardmetal-to-metal impact on severe bottoming.

There is a need for an improved hydraulic suspension unit whichaddresses the conflicting requirements it is asked to fill with respectto compression damping. These include controlling the onset of initialride motions, whether initiated by terrain changes or control inputs,and limiting the maximum velocity allowed in compression thus preventingharsh metal-to-metal bottoming. It is also desired that compressiondamping be accomplished while minimizing the transmission of bumpimpacts to the chassis. An object of the present invention is to providean improved hydraulic suspension unit for a vehicle which addressesthese conflicting requirements it is asked to fill.

These and other objects are attained by the improved hydraulicsuspension unit for a vehicle of the present invention, the suspensionunit comprising first and second members arranged in telescopingrelation with one another for relative movement along a longitudinalaxis of the suspension unit responsive to the relative motions between avehicle wheel and the vehicle body compressing and extending thesuspension unit. Means containing a hydraulic liquid are provided. Thecontaining means include a first chamber containing hydraulic liquid incompressive force transmitting relation between the first and secondmembers. The volume of the first chamber is decreased and increased withrelative movement of the first and second members toward and away fromone another along the longitudinal axis, respectively.

The containing means further includes a reservoir containing hydraulicliquid and passage means connecting the first chamber and the reservoirto permit the flow of hydraulic liquid between the first chamber and thereservoir. The reservoir includes a movable wall which can be moved backand forth to increase and decrease the volume of the reservoir as afunction of the hydraulic liquid flowing to and from the reservoir,respectively.

The suspension unit further comprises spring means for resilientlybiasing the movable wall against the hydraulic liquid in the reservoirwith a force which is a function of the amount of movement of the springmeans and in turn the position of the movable wall and volume of thereservoir. The spring means stores energy upon movement of the movablewall increasing the volume of the reservoir with the flow of hydraulicliquid to the reservoir. Stored energy is released by the spring meansupon movement of the movable wall decreasing the volume of the reservoirwith the flow of hydraulic liquid from the reservoir to the firstchamber.

Compression damping means are provided for damping the flow of hydraulicliquid from the first chamber to the reservoir when the suspension unitis compressed to cause relative movement of the first and second memberstoward one another along the longitudinal axis decreasing the volume ofthe first chamber. Rebound damping means are also provided for dampingthe flow of hydraulic liquid to the first chamber resulting from thespring means releasing energy stored therein by moving the movable wallto decrease the volume of the reservoir and flow hydraulic liquid fromthe reservoir to the first chamber for extending the suspension unit.The rebound damping means allows relative movement of the first andsecond members away from one another for extending the suspension unitby external forces on the suspension unit without resistance from therebound damping means while continuing to damp the flow of hydraulicliquid to the first chamber from the reservoir resulting from release ofstored energy of the spring means. The rebound damping means includes arebound damping valve which is movable in response to pressure of thehydraulic liquid thereon for opening and closing the passage means fromthe reservoir to the first chamber during release of stored energy fromthe spring means.

In order to provide a more flexible spring means with more tuningcapability, the spring means of the suspension unit may be anycombination of air, coil or elastomer springs, which can be separatelyadjusted for preload, providing maximum tuning flexibility withoutresorting to physically changing components. In a disclosed embodimentof the suspension unit, the spring means includes a pressurized gasarranged in an enclosed space in the suspension unit for acting on themovable wall of the reservoir. A coil spring acting on the movable wallcan also be provided in the enclosed space containing the pressurizedgas. Means are also provided for separately adjusting a preload orspring characteristic of each of the gas spring and the coil spring ofthe spring means.

A further feature of preferred embodiments of the suspension unit isthat the passage means directs all of the flow of hydraulic liquid fromthe first chamber to the reservoir via the compression damping means anddirects all of the flow of hydraulic liquid from the reservoir to thefirst chamber via the rebound damping means. Forcing 100% of the shockfluid displaced by extension or compression of the suspension unitthrough a single path, through the rebound damping means or through thecompression damping means, allows more accurate and consistent dampingcontrol. The spring means is arranged to act directly on the movablewall of the reservoir, causing the fluid pressure to act on thecross-sectional area of the shock shaft forcing the shock to extend orresist compression. The movable wall may take the form of a reservoirpiston, a resilient bladder or a flexible diaphragm. With thisarrangement, the spring force and rebound damping have a directrelationship with each other that allows unique manipulationcapabilities of their interaction.

By properly selecting the shaft/reservoir diameter ratio, the springmeans, whether air, steel or elastomer, can have a mechanical advantage(or disadvantage) when acting on the shock shaft through the reservoirmovable wall, allowing flexible packaging.

The maximum speed of expansion of the suspension unit due to release ofstored energy from the spring means is controlled according to theinvention by means for adjustably limiting the maximum flow area forhydraulic liquid flowing past the rebound damping valve from thereservoir to the first chamber when the rebound damping valve is open.This means for adjustably limiting the maximum flow area in a disclosedembodiment includes a mechanical stop limiting the opening extent of therebound damping valve, and externally accessible means for adjusting theposition of the stop.

Control of the hydraulic liquid pressure necessary for opening therebound damping valve to permit the flow of hydraulic liquid from thereservoir to the first chamber and release of stored energy of thespring means is accomplished according to the invention by externallyaccessible means for adjustably, resiliently biasing the rebound dampingvalve in a closed position. In one form of the invention, the rebounddamping valve is a poppet valve. The externally accessible means foradjustably, resilienting biasing includes a coil spring and means foradjusting a preload on the coil spring resiliently biasing the poppetvalve in the closed position.

A performance characteristic of the hydraulic suspension unit of thepresent invention is that the rebound damping valve only affects therebound velocity when such velocity is due to the force imparted by thespring means when it is returning stored energy after some initialcompression. The magnitude of the stored energy can vary greatly and canbe simply due to the force needed to support the static, sprung weightof the vehicle, or to the further compression of the suspension due tocornering, braking, bumps or other terrain variations. The extension, orrebound velocity of the shock is not effected or resisted by the shockabsorber, if the rebound motion is due to external forces extending theshock or suspension. For example, if one end of the vehicle were to belifted suddenly by skyhooks, the suspension unit of the presentinvention would not resist the immediate downward movement of the wheelsas they come off the ground.

This effect allows the wheels to the extension limit of the suspensionunit to follow small or large depressions in the surface of the terrain,maintaining traction and control, yet during any movement involving thereturn of stored energy from the spring, full rebound control is alwaysattained. Suspension geometry can also cause forces to extend the shockabsorber, as in certain anti-dive or anti-squat applications. Theseforces are also allowed to extend the suspension unit to its extensionlimit without the resistance of damping. The feature permitting externaladjustment of the rebound damping characteristics makes the suspensionunit of the invention particularly suited for use in lightweightvehicles such as bicycles and motorcycles where the rider weight is arelative large percentage of total sprung weight of the vehicle.However, the use of such a feature is not necessary to realize improvedperformance and the suspension unit of the invention is also useful inother vehicles.

A compression damping means in the disclosed embodiments includes acompression damping valve which is movable in response to pressure ofthe hydraulic liquid thereon for opening and closing the compressiondamping valve for controlling the flow of hydraulic liquid from thefirst chamber through the passage means to the reservoir duringcompression of the suspension unit. Means are also provided foradjustably biasing the compression damping valve in its closed positionfor controlling the hydraulic pressure and hence compressive force onthe suspension unit necessary for opening the compression damping valveto permit the flow of hydraulic liquid from the first chamber throughthe passage means to the reservoir and the compression of the suspensionunit. The compression damping valve is in the form of a flexible disc inthe disclosed embodiments. The means for adjustably biasing applies anadjustable preload on the disc to affect the hydraulic pressurenecessary to deflect the disc and open the compression damping valve.

The maximum speed of compression of the suspension unit is controlled byadjustably limiting the maximum flow area for hydraulic liquid flowingfrom the first chamber to the reservoir when the compression dampingvalve is open. An adjustment means for this purpose in a disclosedembodiment includes a mechanical stop limiting the opening extent of thecompression damping valve, and externally accessible means for adjustingthe position of the stop.

In one embodiment of the invention, the means for adjustably limitingthe maximum flow area includes an additional valve located in thepassage means upstream of the compression damping valve with respect tothe flow of hydraulic liquid from the first chamber to the reservoir.Externally accessible means are provided for adjusting the extent whichthe additional valve restricts the flow of hydraulic liquid in thepassage means during compression of the suspension unit. In thedisclosed embodiment this additional valve is in the form of a needlevalve. Thus, externally accessible means are provided for independentlyadjusting the amount of damping provided by each of the compressiondamping means and the rebound damping means.

Another feature of the invention is that each of the compression dampingmeans and the rebound damping means of the hydraulic suspension unitacts as a check valve against the flow of hydraulic liquid in theopposite direction than that which is damped thereby. Further, therebound damping valve is preferably arranged for movement so as todisplace hydraulic liquid on the first chamber side of the rebounddamping valve during opening of the valve. The volume of the rebounddamping valve and its linear travel during opening are selected toprovide displacement of a predetermined volume of hydraulic liquid andhence a predetermined expansion of the suspension unit during opening ofthe valve.

These and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in connection with the accompanying drawings which show, forpurposes of illustration only, several embodiments in accordance withthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view in cross-section along the longitudinal centeraxes A--A and B--B of the shock body with shock shaft and reservoirbody, respectively, of a hydraulic suspension unit according to a firstembodiment of the invention;

FIG. 2A is an enlarged view of a portion of the shock body with shockshaft of the suspension unit of FIG. 1 during compression flow;

FIG. 2B is an enlarged view of a portion of the shock body with shockshaft of the suspension unit of FIG. 1 during rebound flow;

FIG. 3 is a graph of force versus deflection for various springs, namelyan air spring, a coil spring and a combined air and coil spring;

FIG. 4A is a side view, partially in cross-section through alongitudinal center axis C--C of a hydraulic suspension unit accordingto a second embodiment of the invention;

FIG. 4B is a side view, partially in cross-section through longitudinalcenter axes of the shock body with shock shaft and the reservoir body ofa hydraulic suspension unit according to a third embodiment of theinvention;

FIG. 5 is a side view, partially in cross-section through longitudinalcenter axes of the shock body with shock shaft and each of dualreservoirs of a hydraulic suspension unit according to a fourthembodiment of the invention;

FIG. 6 is a graph of force versus spring deflection showing the effectsof spring preload;

FIG. 7 is a graph of force versus spring deflection showing the effectsof air volume changes on spring rate;

FIG. 8A is a side view, partially in cross-section through longitudinalcenter axes of a shock body with shock shaft and a reservoir body of ahydraulic suspension unit according to a fifth embodiment of theinvention, the suspension unit having a diaphragm separator as a movablewall of the reservoir, and the suspension unit being shown in acompressed position;

FIG. 8B is a side view of a portion of the suspension unit as shown inFIG. 8A depicting the suspension unit in an extended position;

FIG. 9 is a side view, partially in cross-section through a longitudinalcenter axis of a reservoir body of a hydraulic suspension unit accordingto a sixth embodiment of the invention, the suspension unit having arebound damping valve and compression damping valve arranged in theupper end of the reservoir body with four-way, external adjustmentthereof being provided;

FIG. 10A is an enlarged view of a portion of the suspension unit of FIG.9 during compression flow;

FIG. 10B is an enlarged view of a portion of the suspension unit of FIG.9 during rebound flow;

FIG. 11A is an enlarged view of a portion of the rebound damping valveof the embodiment of FIGS. 9, 10A and 10B wherein the valve isconfigured to allow flow to occur immediately upon any lineardisplacement thereof;

FIG. 11B is a view of a rebound damping valve like that in FIG. 11A butwith a valve configuration which requires a linear travel of 0.1 inchbefore allowing any flow;

FIG. 12A is a side view, partially in cross-section through longitudinalcenter axes of a hydraulic suspension unit like that depicted in theembodiment of FIG. 1, further provided with an external auxiliary springacting to extend the shock without forcing hydraulic liquid through therebound damping valve;

FIG. 12B is a side view, partially in cross-section along longitudinalcenter axes of a suspension unit like that of FIG. 1 but with aninternal auxiliary spring being provided in a chamber of the shock bodycontaining hydraulic liquid to extend the shock without forcinghydraulic liquid through the rebound damping valve;

FIG. 13 is a side view, partially in cross-section through longitudinalaxes of a suspension unit similar to the suspension unit of FIG. 1 butwith an internal auxiliary spring and an auxiliary divider piston beingprovided to extend the shock without forcing hydraulic liquid throughthe rebound damping valve; and

FIG. 14 is a schematic illustration of a hydraulic suspension unitbetween a wheel and the body of a vehicle, the wheel traveling along asurface having a two inch drop.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

Referring now to the drawings, a hydraulic suspension unit 60 accordingto a first embodiment of the invention is depicted in FIGS. 1, 2A and2B. The suspension unit 60 comprises first and second members in theform of a shock body 4 and a shock shaft 8 arranged in telescopingrelation with one another for relative movement along a longitudinalaxis A--A of the suspension unit responsive to relative motions betweena wheel of a vehicle and the vehicle body compressing and extending thesuspension unit. Apertures 61 and 62 at the upper end of the shock shaft8 and the lower end of the shock body 4, respectively, permit connectionof the suspension unit between a vehicle body 64 and a wheel 63 thereofin the manner shown schematically in FIG. 14. The shock body 4 and shockshaft 8 in FIG. 1 are shown in an extended position of the suspensionunit.

A hydraulic liquid such as oil is contained in the suspension unit 60within a first, interior chamber 3 in the shock body 4 where thehydraulic liquid is in compressive force transmitting relation betweenthe shock shaft 8 and shock body 4. The volume of the interior chamber 3is decreased and increased with relative movement of the shock shaft andshock body toward and away from one another along the longitudinal axisA--A. A fluid passage 25 in the shock shaft 8 and a reservoir body 24connects the interior of chamber 3 with a hydraulic liquid reservoir 19in the reservoir body 24. The reservoir 19, passage 25 and chamber 3 arefilled with the hydraulic liquid. The reservoir includes a movable wallin the form of a piston 23 which can be moved back and forth along theaxis B--B of a cylinder defined within the reservoir body 24 to increaseand decrease the volume of the reservoir 19 as a function of the volumeof hydraulic liquid flowing to and from the reservoir with a decrease orincrease in the volume of chamber 3 upon compression or expansion of thesuspension unit. A sealing arrangement 40 is provided between the shockbody 4 and the shock shaft 8.

The piston 23 is resiliently biased against the hydraulic liquid in thereservoir 19 by a spring formed by a coil spring 20 and a pressurizedgas, air for example, located within an enclosed space 65 on the lowerside of the piston 23 in reservoir body 24 as depicted in FIG. 1. A seal50 is provided between the outer periphery of the piston 23 and the wallof the cylinder in the reservoir body 24 for effectively separating thepressurized air and the hydraulic liquid on respective sides of thepiston 23 without restricting movement of the piston in the cylinder.

The spring formed by coil spring 20 and the pressurized air in theenclosed space 65 resiliently biases the piston 23 with a force which isthe function of the amount of movement, e.g. compression of the spring20 and the volume of enclosed space 65 and in turn the position of thepiston 23 and the volume of the reservoir 19. That is, the spring storesenergy upon movement of the piston 23 in response to pressurizedhydraulic liquid increasing the volume of the reservoir 19 with the flowof hydraulic liquid to the reservoir from compression of the shock dueto an increase in compressive force on the suspension unit. When thisforce or load on the suspension unit is reduced, the spring releases itsstored energy by moving the piston 23 upward to decrease the volume ofthe reservoir 19 with the flow of hydraulic liquid from the reservoir tothe interior chamber 3 by way of fluid passage 25 thereby expanding thesuspension unit to restore a balance of force on the hydraulic liquid inthe suspension unit from the external load on the suspension unit andthe force of the spring-loaded piston 23.

By using a combination of spring media, it is possible to have aninfinite number of adjustment combinations. The linear rate of the steelcoil spring 20 is combined with the rising rate characteristic of thepressurized air as shown in FIG. 3. Tuning flexibility with respect tothe spring rate of the combination of springing media is achieved byproviding adjustment for each of the spring media. For coil spring 20,coil spring preload adjuster 21 allows an adjustable preload to beapplied to the coil spring 20 by rotating the threaded preload adjuster21 threadedly received in the end of the reservoir body 24 to define anend of enclosed space 65. FIG. 6 illustrates the effects of springpreload on the force versus deflection curve of coil spring 20. Thecharacteristic for the 800 pounds/inch coil spring with no preload iscompared with that for the spring preloaded 0.2 inch, that is byadvancing preload adjuster 21 into the reservoir body 24 a distance of0.2 inch along the axis B--B thereby compressing and preloading the coilspring.

The same type of adjustment is provided for the air spring by air volumeadjuster 22 for changing the air volume within the enclosed space 65 bythreadedly moving the adjuster 22 with respect to the preload adjuster21 and enclosed space 65. This enables a change in the rate ofprogression of the air spring as deflection increases. The effects ofchanges in the rate of progression of the air spring due to variationsin the available air volume are shown in FIG. 7.

Thus, in the embodiment of FIG. 1, for packaging and tuning flexibility,both the coil spring and air spring are packaged in the same reservoirwith dual, coaxial adjusters for the respective springs. However, two ormore of the aforementioned springs can be arranged in respectivereservoir bodies 24 and 24' as shown in the embodiment of FIG. 5. Also,as shown in the embodiment of FIG. 9, a tapered spring 20t can be usedfor more compact packaging and rising rate. An elastomer could also beused in place of the coil spring in these embodiments. In the embodimentof FIG. 4A the reservoir 19, piston 23 and coil spring 20 are arrangedwithin the shock shaft 8 along the axis A'--A' of the suspension unit.The embodiment of FIG. 4B is similar to that in FIGS. 1, 2A and 2B butdoes not include air valve adjuster 22.

The movable wall of the reservoir 19 in the embodiment of FIG. 1 is inthe form of piston 23. However, the movable wall could have other forms,such as a resilient bladder 26 formed of rubber, for example, as in thereservoir body 24' in the embodiment of FIG. 5, or a flexible diaphragm27 as in the embodiment of FIGS. 8A and 8B. This fluctuating diaphragm27 is advantageous in that it will have a quicker response to allinputs, avoiding a loss of sensitivity common with a divider piston, orto a lesser degree with a rubber bladder. The high sensitivity possibleto even the smallest inputs offers improved ride characteristics andhandling.

The diaphragm 27 in the embodiment of FIGS. 8A and 8B consists of amolded rubber or rubberized material arranged to lie in a torus shapewhen at the extremes of its travel. The center of the diaphragm 27consists of a circular disc 28 made of metal or other stiff material. Ifused with a coil or elastomer spring, a coil 20 is shown in FIGS. 8A and8B, the periphery of the disc 28 may be turned as shown, to a dishshape, to provide a means for centering the spring.

The hydraulic suspension unit 60 of the present invention furthercomprises compression damping means for damping the flow of hydraulicliquid from the first chamber 3 to the reservoir 19 when the suspensionunit is compressed to cause relative movement of the shock body 4 andshock shaft 8 towards one another along the longitudinal axis A--Adecreasing the volume of the first chamber 3. In the embodiment of FIGS.1, 2A and 2B, the compression damping means includes a compressiondamping valve in the form of a disc 10 which is movable in response topressure of the hydraulic liquid thereon for opening and closingpassages 25A and 25B of the fluid passage 25 in a valve body 12 of theshock shaft 8. As shown in FIGS. 1, 2A and 2B, in order for the shockabsorber of the suspension unit 60 to compress, the pressure of thehydraulic liquid in the chamber 3 must rise to the extent that it candeflect the disc 10 allowing the liquid to flow past, and into thereservoir 19, thus compressing the spring. By means of a compressiondamping adjuster 11 threaded into the valve body 12, a preload on thedisc 10 can be increased, thus increasing the pressure necessary todeflect the disc 10, to allow the shock to move. Since this controls theinitial force necessary to compress the shock, it serves as an effectiveway to control the compression damping that occurs at low shock shaftvelocities.

In the extreme, the adjuster 11 can be configured so that, at the limitof adjustment, the disc 10 will be clamped between the adjuster 11 andthe valve body 12, thus preventing any deflection of the disc. In thiscondition, the shock absorber can not be compressed, as it is no longerpossible for liquid flow to occur, hydraulically locking the shockabsorber. The adjustment is effected in the embodiment of FIGS. 1, 2Aand 2B by turning the adjuster shaft with knob 5A connected theretowhich in turn rotates adjuster 11 in valve body 12 by projections 5B onthe shaft engaged in slots in adjuster 11.

High speed compression damping and adjustment thereof are attained by amanipulation of the total amount of flow area allowed under compression.By limiting the total flow area, an orifice effect can be created,through which compression forces can increase exponentially with shaftvelocities, thereby allowing precise control over shaft velocities.These effects are achieved in the embodiment of FIGS. 1, 2A and 2B, bylimiting the total amount of deflection of the disc, with an annularmechanical stop 11A incorporated into the compression damping adjuster11. Thus, the disc is still allowed to deflect in response to low shockshaft velocities, but shaft velocities can be limited by the orificeeffect created. A poppet type valve can also be used, with an initialspring preload, and a travel limit, to control maximum flow area.

While the foregoing means of controlling the high speed shaft movementsof the suspension unit during compression can be effective, anadditional feature of the invention depicted in the embodimentillustrated in FIGS. 9, 10A and 10B allows for much finer adjustmentcapabilities, and more independent control of high speed shaft movementsduring compression. This is accomplished using an adjustable orifice orneedle valve 13, inserted into the compression flow path 25D leading tothe disc 10 and reservoir 19. With this arrangement, the effect of thehigh speed adjustment remains independent from the effects of the lowspeed adjustment. As the hydraulic liquid is forced into the reservoir19 through passage 25D, it must first pass through the orifice needlevalve 13, before it can deflect the compression disc 10 and compress thespring means. If the shock shaft movement is below a certain velocity,the needle valve 13 cannot present enough of a flow restriction for thesmall flow volume, and therefore has no effect on the damping force.This leaves the disc 10 to be responsible for providing damping force,as it must deflect in order for any shaft movement to occur. As shaftvelocity increases, the compression disc 10 remains deflected and flowincreases until the needle valve 13 does become a flow restriction,thereby creating damping force at those shaft velocities. If the needlevalve 13 is threaded into the reservoir body 24, rotation causes thevalve to translate, thus varying the available flow area, andsubsequently, the high speed damping force.

The hydraulic suspension unit 60 according to the embodiment of theFIGS. 1, 2A and 2B further comprises rebound damping means in the formof rebound valve 1, a poppet type valve, and a cooperating rebound valveseat 6 formed in the valve body 12. The rebound damping means damps theflow of hydraulic liquid to the first chamber 3 resulting from thespring means releasing energy stored therein by moving the piston 23 todecrease the volume of the reservoir 19 and flow hydraulic liquid fromthe reservoir to the first chamber for extending the suspension unit.The rebound damping means allows relative movement of the shock body 4and shock shaft 8 away from one another along the axis A--A forextending the suspension unit to the extension limit by external forceson the suspension unit without resistance from the rebound damping meanswhile continuing to damp the flow of hydraulic liquid to the firstchamber 3 from the reservoir 19 resulting from release of stored energyof the spring means. The rebound damping valve 1 is movable in responseto pressure of the hydraulic liquid thereon for opening and closing thepassage 25C at the rebound valve seat 6 for controlling the flow ofhydraulic liquid through the fluid passage 25 from the reservoir 19 tothe first chamber 3 during release of stored energy from the springmeans formed by the coil spring 20 and the pressurized air in enclosedspace 65.

The primary function of rebound damping with rebound valve 1 is todampen the return of energy that has been stored by the springing media,coil spring 20 and the pressurized air in enclosed space 65, due tocompression of the spring. As the suspension is compressed further, moreenergy is stored which must be released as soon as possible. Thereforethe rebound damping valve 1 is preferably of a type that, knowing themaximum possible energy stored in any given springing system, should beable to limit the rebound shaft velocity to a known maximum, for a knownspring and known vehicle sprung weight (since that is what the returningenergy must push against). This maximum rebound velocity can becalculated based on the maximum desirable upward acceleration of thesprung weight or it can be based on empirical data, choosing a maximumvelocity that does not create uncomfortable ride motions, or allow adangerous recoil. With conventional shocks, setting the rebound dampingin this way would create the "packing down" phenomena described earlieras the rebound damping would be too high to allow the wheel to returnfast enough for multiple bumps.

A suspension unit of the present invention is able to utilize theaforementioned type of rebound damping, without suffering from "packingdown". The rebound damping means of the suspension unit of the presentinvention is configured, in combination with the springing means, toallow the wheel to fall when it is unloaded, such as when encountering adepression, without impeding the shaft velocity with rebound dampingresistance. In other words, it will allow the wheel to fall solely underthe influence of the mass being attracted by gravity, even if that rateis faster than the spring can extend the shock against the force of therebound damping. This falling of the wheel is possible while retainingthe ability to limit rebound velocity against spring force, as describedearlier.

The rebound valve 1 is configured so that the hydraulic liquid flow inthe rebound direction can only take place if the liquid can push thepoppet type rebound valve 1 against pressure from a rebound spring 2.The maximum opening or flow rate of this valve is used to limit themaximum rebound velocity of the shock shaft from release of storedenergy by the spring means. As the spring means pushes directly on thehydraulic liquid, and thus the rebound valve 1, no cavitation can occur,and precise control of the spring energy is realized. In the event thatthe wheel encounters a sudden depression, the weight of the wheel andsuspension will attempt to fall freely, unless resisted by rebounddamping. With the present invention, the rebound valve 1 remains closedmomentarily, as a temporary vacuum is allowed to form on the downstreamside of the rebound valve 1, in chamber 3 created by the surroundingshock body 4. The formation of this vacuum allows the wheel to fallfreely, resisted only by the negligible force of the vacuum force itselftrying to retract the shock, and the initial cling/shear properties ofthe hydraulic liquid on the internal surfaces of chamber 3. This allowsthe wheel to follow the terrain surface more accurately, resulting inbetter traction, better cornering grip and control. The free fall of thewheel and the resultant formation of this vacuum all take place in afraction of a second. Thus, the existence of the vacuum is fleeting asthe rebound valve 1 starts to flow oil and begins to fill chamber 3.

The rebound valve 1 is provided with an external adjustment, threadedrebound adjuster 5, which can be rotated external to the shock absorber,causing it to translate in the shock body for varying the maximumorifice flow area of the valve 1 and thus the maximum allowable reboundvelocity. This translation moves a travel limiting stop 9 for therebound valve 1, and thus varies the high speed rebound damping force.At lower rebound shaft velocities, the total flow area available throughthe valve 1 is not a limiting factor, thus this adjustment has no effecton the low speed rebound damping, or the "free fall" characteristics.

The embodiment disclosed in FIGS. 9, 10A and 10B further includes anadditional, separate external adjustment to manipulate the "free fall"characteristics of the shock, as well as the intermediate speed rebounddamping force. As mentioned earlier, the pressure of the rebound valve 1against its seat 6 is controlled by the pressure of the preload spring2. Once the rebound valve 1 begins to open, intermediate shaftvelocities are controlled by the rate of spring 2. Both of thesecharacteristics can be modified by rotating threaded adjuster 7 in theembodiment of FIGS. 9, 10A and 10B. The resultant translation serves tovary the seat pressure and rate rise of spring 2 which results in theadjustability described above. This adjustment can be made externally ofthe suspension unit.

The suspension unit of the invention then, can be tuned to offer noresistance to the shock being extended provided that the forces tryingto extend the shock are externally pulling the shock apart, as in sprungweight (wheel, tire, suspension components) falling due to gravity.Other forces can be created in the suspension geometry to produceexternal forces that tend to pull the shock apart, i.e. anti-squat oranti-dive. However, if the force trying to extend the shock is theresult of the spring means returning stored energy, then this energywill be dissipated with rebound damping as the spring means attempts toflow oil through the rebound valve 1 in order to extend the shock.

When a vacuum is formed in chamber 3, the pressure differential acrossthe rebound valve 1 is increased, encouraging the valve to open to allowoil to displace the vacuum as soon as possible. Thus, the surface areaof the rebound valve 1 exposed to the vacuum can be manipulated tomodify the additional effect of the pressure differential, when a wheelis unloaded. After the shock is compressed, the spring means willattempt to return its stored energy as described earlier by displacingthe rebound valve 1 against pressure from the spring 2. Thus, the areaof the rebound valve 1 that is exposed to this pressure, determines thetotal force (pressure multiplied by area) exerted on the rebound spring2. However, the rebound valve 1 is preferably configured so that a muchlarger surface area is exposed to the downstream, or low pressure sideof the flow than is exposed to the upstream or high pressure side of theflow. In the disclosed embodiment of FIGS. 1, 2A and 2B, for example,the ratio of exposed downstream surface area to exposed upstream surfacearea of the rebound valve 1 is about 3:1, but other ratios could beused. Preferably this ratio is at least 1.5:1. Thus, in the presence ofthe vacuum which forms due to the "free fall" described earlier, thisvacuum, while very small in terms of absolute pressure, can act on arelatively large surface area of the rebound valve 1, to create asignificant force with which to assist in opening the rebound valve 1against the force of rebound spring 2, thus reducing the rebound dampingforce during these conditions and allowing quicker flow of hydraulicfluid returning to the chamber 3 so that the suspension unit is ready incase of impact tending to compress the suspension unit. There is nodanger of a dangerous, undamped recoil occurring as the wheel must beunloaded in a free fall condition in order for the vacuum to form. Aslong as the wheel is unloaded there is nothing for the spring recoil topush against, making it impossible for a recoil force to be imparted tothe chassis. Thus, the ratio of surface area exposed to the highpressure side of the flow versus the surface area exposed to the lowpressure side of the flow provides another means for automaticallymodifying the rebound damping characteristics of the shock to suitchanging conditions and demands on damping force.

The characteristics of the rebound damping during "no flow" or openingof the rebound valve can also be further enhanced by manipulating thevolume and linear travel of the rebound valve 1 itself to provide aprecise amount of shock movement in the rebound direction, withoutoffering resistance due to damping, even if the movement is a result ofrelease of spring energy. Due to the design of the rebound valve 1, itcan be tuned to allow a small, but exact amount of shock travel, whileoffering a reduced, but adjustable amount of rebound resistance. This isdue to the fact that the rebound valve 1 limits high speed shaftmovement by adjusting the orifice size available to flow hydraulicliquid, by limiting its linear travel against the flow of liquid, butfor small movements of the valve, there is little or no flow across therebound valve 1, until the shaft movement is sufficient to displace theentire volume of the rebound valve, and it becomes a flow restriction.

For example, the shock shaft 8 shown in the embodiment of FIGS. 1, 2Aand 2B could have a one inch diameter, resulting in a cross-sectionalsurface area of 0.785 square inch Therefore, any shock shaft movementmust be accompanied by an equivalent liquid volume displacement equal tothe shaft area times the shaft movement. In this case the rebound valve1 has a 0.5 inch diameter, and its area is 0.169 square inch. Thus, a0.1 inch movement of the shock shaft 8 results in a volume displacementof 0.785×0.1=0.0785 cubic inch. The rebound valve 1 has to travellinearly by 0.0785/0.196=0.400 inch, in order to accommodate thismovement without offering a flow restriction. Thus, the only resistance,if any, to this small shaft movement, is the pressure from spring 2,which can easily be adjusted in the preferred embodiment.

In this way, the shock absorber can be tuned to allow quicker responseto small wheel movements, and such movements themselves can be preciselycontrolled due to the exact nature of hydraulics, and the ease ofadjusting the force from spring 2. Careful selection of the ratiobetween the diameter and thus area of shaft 8, and the diameter andlinear travel of rebound valve 1 allow exact characteristics to beobtained.

A further manipulation can be achieved by altering the rate of change offlow area versus the linear travel of the rebound valve 1. For example,the rebound valve 1 in the embodiment of FIGS. 9, 10A, 10B and 11Aallows flow to occur immediately upon any linear displacement, whereas arebound valve la, as depicted in FIG. 11B, requires a linear travel of0.1 inch before allowing any flow. This feature is further used tocharacterize the effects of the volume displacement of the reboundvalve.

FIG. 14 schematically illustrates a hydraulic suspension unit between avehicle wheel 63 and the body 64 of the vehicle, such as a bicycle ormotorcycle, the wheel traveling along a surface having a two inch drop.Assume a 1:1 motion ratio between wheel and shock and that thesuspension unit is compressed two inches statically before encounteringthe two inch vertical drop with the vehicle traveling at a velocity of30 miles per hour, e.g. 528 in/sec. As a first example, where thesuspension unit is one having a conventional rebound dampingcharacteristic, enough to prevent most dangerous recoils, assume thatthe maximum allowable wheel rebound velocity is limited to 5 inches persecond to insure that no "launching" of the vehicle can occur. In aconventional shock this rebound damping would slow the wheel's descentinto the two inch depression. Assuming that the wheel could accelerateinstantly to 5 in/sec, it would take 2 in/(5 in/sec)=0.4 second for thewheel to reach the ground. Since the vehicle is traveling at a speed of528 in/sec, the vehicle would traverse (528 in/sec)×(0.4 sec)=211.2inches, before the wheel would reach the ground. In reality, due to thefact that the wheel cannot accelerate instantly, as assumed for thiscalculation, this distance would be much greater.

In contrast, where the hydraulic suspension unit is one according to thepresent invention, while limiting shaft velocity to 5 in/sec if due tospring force, in this case the wheel and tire are allowed to "free fall"into the depression. Using standard physics equations to solve for timeand maximum velocity of the free fall of objects in space:

v=gt where v=velocity

h=1/2 gt² h=height

g=gravity =32 ft/s² =384 in/s²

t=time

and rearranging the second equation to solve for time t, ##EQU1## forthe wheel to reach the ground. Using the same vehicle velocity as in thefirst example, the vehicle would travel (528 in/sec)×(0.102 sec)=53.8inches before the wheel touched the ground, compared to 211.2 inches forthe damped wheel. The maximum wheel velocity can be calculated using theequation v=gt=(384 in/sec²)×(0.102 sec)=39.2 in/sec, compared to themaximum velocity of 5 in/sec in the previous case. In this regard, it isnoted that if the normal rebound damping in the first example were to bereduced to allow the free fall velocities of this example with thepresent invention, the result would be uncomfortable and potentiallydangerous ride motions under conditions where high rebound damping isnecessary to control the return of stored energy from the springingsystem.

The relationship between spring force and rebound damping is furthermanipulated according to an additional feature of the invention byemploying an auxiliary spring acting to extend the shock without forcinghydraulic liquid through the rebound valve 1. The auxiliary spring canbe configured concentrically external to the shock shaft as shown in theembodiment of FIG. 12A, or internal to the shock absorber as shown inthe embodiments of FIGS. 12B and 13. The auxiliary spring can be a coilspring, gas, elastomer, or other medium. The auxiliary spring provides aspring assist to the "free fall" characteristics of the suspension unitas discussed above. For example, if an auxiliary spring 29 in theembodiment of FIG. 12A were configured to have 30% of the total springrate required by the vehicle, then a force equivalent to spring ratetimes deflection=200 lb/in×2 in=400 lbs is pushing the suspensiondownward, without resistance from rebound damping. In the example of thetwo inch drop discussed with reference to FIG. 14, this would result inthe following. As in the previous math example:

v=velocity

h=height

g=gravity=32 ft/sec² =384 in/sec²

t=time,

Also w=10 lb (weight of wheel/tire)

a=acceleration

k=200 lb/in (aux spring rate)

x=2 in (spring deflection).

From the concept of the conservation of energy, the equation set forthbelow can be written to relate the potential energy of the wheel due tothe auxiliary spring pressure, to the kinetic energy the wheel will haveafter being put into motion by the auxiliary spring. This equation canbe solved to find the velocity v which the auxiliary spring will impartto the wheel/tire and, in turn, the time it takes for the tire to reachthe ground. In this case, the effects of gravity producing the free fallvelocity found in the previous example are ignored. KE=KineticEnergy=wv² /2g=Potential Energy=PE=1/2 kx²

thus, wv² /2g=1/2 kx².

Solving this equation for v:

v= kx² g/w!

v= (200 lb/in) (2 in)² (384 in/s²)/(10 lb)!

v=175.3 in/sec.

If the average velocity is then v/2=87.65 in/sec, the time t can befound by dividing distance traveled by average velocity=2 in/87.65in/sec=0.023 seconds for the tire to reach the ground. This compares tothe 0.4 sec of the first example for the conventional shock absorber andthe 0.102 sec of the "free fall" example of the present invention.

Thus, if the vehicle has a forward speed of 528 in/sec, it would travel(528 in/sec) (0.023 sec)=12.12 inches after crossing the two inch dropoff, before the tire reaches the ground. This is compared to the 211.2inches of the first example and the 53.8 inches in the free fallexample. By allowing the tire to re-establish contact with the groundquicker, control and handling are increased, and ride comfort enhanced.

It is noted that in the instance of the vehicle wanting to reboundquickly due to a high amount of stored spring energy, the reboundvelocity would be controlled as previously described, and limited to adesirable velocity. This is the case because the percentage and rise ofthe spring rate from the auxiliary spring is selected to be a minorpercentage of the total spring rate provided by the primary spring meansand the auxiliary spring. In the disclosed example the auxiliary springonly provides thirty percent of the total spring rate. Obviously, thepercentage and rise of the spring rate used for the auxiliary springmust be carefully chosen against the ratio of sprung to unsprung weightas well as intended function of the vehicle. Too high of a percentage ofthe total spring rate in the auxiliary spring could cause dangerousundamped extension movements of the shock absorber. For example, if theauxiliary spring was able to provide 100% of the spring force, thisspring could return its stored energy with no resistance from therebound damping, due to the fact that this spring is not required topush hydraulic liquid through the rebound valving, as is the case withthe primary spring means.

In the disclosed configurations, when the shock is compressed, both theprimary and auxiliary springing systems must be compressed in equalamounts (or equal percentage depending on the hydraulic ratio drivingthe primary spring). This is always the case regardless of conditions.Thus, when the suspension unit is compressed fully, the primary springmeans will always be forced to push the total amount of hydraulic liquidback through the rebound valve, insuring that adequate rebound dampingis always available. Due to the fact that the auxiliary spring onlyprovides a minor percentage of the total spring rate, it is unable toapply enough force to the chassis, even when fully deflected, to cause adangerous recoil action to occur. The primary facts effecting thepercentage of auxiliary spring used are: vehicle configuration, numberof wheels, sprung weight, unsprung weight, on or off road use,competition use, passenger use.

The characteristics of the auxiliary spring and its dynamic relationshipwith the primary spring means and the rebound valving are somewhatdifferent depending upon whether the auxiliary spring is positioned asan external spring 29 as shown in FIG. 12A, or internal to the shock asshown at 29¹ and 29¹¹ in FIGS. 12B and 13, respectively.

More particularly, the variations shown in FIGS. 12A and 12B areidentical in terms of function and operation, because even though thespring 29¹ is internal in FIG. 12B it occupies the same volumeregardless of its state of compression. The variation shown in FIG. 13however, is separated from the hydraulic liquid of the shock with adivider piston 30. This means that the internal volume of the shockabsorber changes at a different rate than in the embodiments of FIGS.12A and 12B, having implications on spring rate as well as compressionand rebound damping.

From the disclosed embodiments of the present invention, it can be seenthat one of the advantages realized with the present invention is that100% of the shock liquid displaced by extension or compression is forcedthrough a single path (through the rebound valve or compression valve),allowing more accurate and consistent damping control. Primary springforce is then arranged as shown in the disclosed embodiments to actdirectly on the reservoir piston or bladder, causing the fluid pressureto act on the cross-sectional area of the shock shaft, forcing the shockto extend or resist compression. With the spring force and reboundvalving arranged in this manner, they have a direct relationship witheach other that allows unique manipulation capabilities of theirinteraction.

By properly selecting the shaft/reservoir diameter ratio, the spring,whether air, steel or elastomer, can have a mechanical advantage (ordisadvantage) when acting on the shock shaft through the reservoirpiston/bladder, allowing flexible packaging. Note that in allembodiments of compression and rebound valving described, in each case,the compression and rebound valves themselves act as check valvesagainst flow in the opposite direction making use of separate checkvalves unnecessary.

The following are examples of various conditions under which theoperation of the hydraulic suspension unit of the present invention iscompared to more conventional solutions. The first example would be avehicle encountering a pothole or depression. It is shown in the abovediscussion with respect to FIG. 14, the present invention allows thewheel to make contact with the ground much sooner, increasing controland the tires' mechanical grip with the surface.

A second comparative example is where a wheel of a vehicle encounters asudden bump or elevation gain in the surface. With a conventional damperwith compromise rebound damping, after the shock compresses due to theterrain rising under it, a large recoil is impending as the spring triesto release the energy stored. Since the rebound damping is based on acompromise, in this instance there is not enough rebound damping toprevent excessively high rebound velocities, resulting in uncontrollableride motions as the chassis is thrust upward, as well as loss ofcontrol, with the possibility that the vehicle may be launched upwardwith sufficient force to cause the vehicle to leave the ground. Incontrast, with the present invention none of the foregoing is possible,due to the fact that the damping has been specifically chosen to limitthe maximum rebound velocity for conditions where the springing systemis returning stored energy. Thus, the resultant ride motions are wellcontrolled, and the recoil sufficiently damped to avoid theaforementioned problems.

A third example is an extension of the second. Once a bump or terrainchange exceeds a certain magnitude, it becomes a jump. Not normallyencountered on public highways, it is nevertheless a very commoncomponent of many off-road car, truck, motorcycle, and bicycle races.For this purpose, a jump is defined as a rapid rise in elevation, suchas a ramp, that causes a vehicle traversing it to leave the groundcompletely with all wheels off the ground. Typically, the problems hereare the same as in the previous example, however, they are magnified inthe case of a jump.

When the vehicle is on the face of the jump, it is typical for thesuspension to compress completely to its limits, to cope with thechanging direction of the vehicle, and the resultant upwardaccelerations. This causes the spring system to store the maximum amountof energy possible, which it will return as soon as the change ofdirection is complete, and the resultant acceleration is diminished.With conventional rebound damping, this return of energy takes place tooquickly, adding an undesirable component of vertical velocity to thevehicle's path, already having a vertical component due to the ramp.

This is particularly dangerous in the rear. After the front of thevehicle has left the face of the jump, the front suspension can nolonger push the vehicle upward as there is no longer a surface to pushagainst. However, the rear of the vehicle and the rear suspension isstill on the ramp. Any additional upward motion in the rear at thispoint has the tendency, not only to raise the rear, but to impart arotational torque on the vehicle inducing the front to nose divepotentially causing the vehicle to flip end over end. Such a phenomenais not uncommon in the previously mentioned racing. Again, withconventional shocks, the rebound damping is usually too compromised toallow the correct amount of rebound control for these conditions. Evenif a compromise is reached that allows acceptable performance undercertain circumstances (or given track conditions), if conditions change,such as a lip being formed at the peak of a jump during the course ofthe race, the delicate balance of the compromise is upset, once againcausing undesirable behavior.

The present invention solves these problems in that the hydraulicsuspension unit allows the rebound damping to be chosen specifically tolimit the maximum rebound velocity induced by the springing system,regardless of the events that lead to the springing system having storedenergy. Therefore the vehicle will be very stable when leaving the jump,and travel in a lower trajectory, again allowing the wheels to return tothe surface earlier, ready for braking, turning or accelerating. Afterthe vehicle leaves the face of the jump, the wheels are allowed to freefall to the extension limit of the suspension, with no resistance fromthe shock absorber. This allows the maximum pressure differential acrossthe rebound valve, helping the valve to open sooner, further helping thewheel descend. This also serves to cause the vehicle to land sooner, asthe wheels impart a downward impulse as they reach the limits ofextension.

A further example of the improved performance of the hydraulicsuspension unit of the present invention as compared with theconventional suspension unit is that of a four-wheeled vehicle in acorner. As the vehicle enters the corner, the side of the vehicle on theoutside of the corner moves downward as the suspension compresses, andupward on the inside as the suspension extends. This action is caused byweight transfer, which allows the inside springs to return some or allof the energy stored due to supporting the vehicle's static weight. Thischassis roll during cornering is resisted by the springs and compressiondamping on the outside, and the rebound damping on the inside. In thisinstance, as long as there is still rebound stroke available, the insidewheel never becomes completely unloaded. Since this is also a case ofenergy being returned by the springing system, the rebound damping isable to retain full control of wheel extension, providing the sharpesthandling response to control inputs. In the event that the inner wheelencounters a depression while in a corner, with the suspension unit ofthe present invention it would still free fall into this depression withno resistance, as soon as the wheel was unloaded.

Thus, it can be seen that the improved hydraulic suspension unit of thepresent invention allows the use of rebound damping in sufficientstrength to control any energy being returned from the spring, allowingshock rebound velocity to be well controlled. Simultaneously, anyunloading of a wheel allows the wheel to free-fall until such wheel isagain in a loaded condition. This combination of attributes greatlyincreases ride comfort and handling control. The use of the auxiliaryspring as described, further assists the tire in maintaining contactwith the surface. The compression damping valve arrangement allowsprecise control over small and large impacts, without imparting rideharshness. The overall effect is one of increased ride comfort, withbetter control of all chassis and wheel movements, resulting in moreconsistent contact pressure between the tire and road surface. Thefeatures of the present invention permitting external adjustment of thespring and rebound damping characteristics as well as the compressiondamping characteristic make the hydraulic suspension unit of the presentinvention well suited for use in light vehicles such as motorcycles andbicycles, where the rider weight is a very large percentage of the totalsprung weight (over 90% in the case of a bicycle). With such a vehicle,it is impossible to choose one spring weight that is suitable for allrider weights. Different rider skill levels also play a large role inthis choice.

While several embodiments of the present invention have been shown anddescribed herein, it will be obvious to one skilled in the art that thepresent invention may be put into practice in many forms and that manymodifications may be made thereto without departing from the spirit ofthe invention. Therefore, this invention is not limited to the foregoingembodiments, but rather by the invention as defined by the followingclaims both literally and through the scope available under the Doctrineof Equivalents.

I claim:
 1. A hydraulic suspension unit comprising:first and secondmembers arranged in telescoping relation with one another for relativemovement along a longitudinal axis of said suspension unit with changesin force on said suspension unit compressing and extending saidsuspension unit within an extension limit of the suspension unit; meanscontaining a hydraulic liquid, said containing means including a firstchamber containing hydraulic liquid in compressive force transmittingrelation between said first and second members without resistingextension of said suspension unit to said extension limit by externalforces on said suspension unit, the volume of said first chamber beingdecreased and increased with relative movement of said first and secondmembers toward and away from one another along said longitudinal axis,respectively, and said containing means further including a reservoircontaining hydraulic liquid and passage means connecting said firstchamber and said reservoir to permit the flow of hydraulic liquidbetween said first chamber and said reservoir, said reservoir includinga movable wall which can be moved back and forth to increase anddecrease the volume of said reservoir as a function of the volume of thehydraulic liquid flowing to and from said reservoir, respectively;spring means for resiliently biasing said movable wall against thehydraulic liquid in said reservoir with a force which is a function ofthe amount of movement of said spring means and in turn the position ofsaid movable wall and volume of said reservoir, said spring meansstoring energy upon movement of said movable wall increasing the volumeof said reservoir with the flow of hydraulic liquid to said reservoir,and said spring means releasing said stored energy upon movement of saidmovable wall decreasing the volume of said reservoir with the flow ofhydraulic liquid from said reservoir to said first chamber; compressiondamping means for damping the flow of hydraulic liquid from said firstchamber to said reservoir when said suspension unit is compressed tocause relative movement of said first and second members towards oneanother along said longitudinal axis decreasing the volume of said firstchamber; rebound damping means for only affecting the rebound velocityof the initially compressed suspension unit when such velocity is due tothe force imparted by the spring means when it is returning storedenergy after some initial compression, said rebound damping meansdamping the flow of hydraulic liquid to said first chamber resultingfrom said spring means releasing energy stored therein by moving saidmovable wall to decrease the volume of said reservoir and flow hydraulicfluid from said reservoir to said first chamber for extending saidsuspension unit, while said rebound damping means and said suspensionunit at the same time not resisting relative movement of said first andsecond members away from one another for extending said suspension unitto said extension limit of said suspension unit by external forces onsaid suspension unit; and externally accessible means for independentlyadjusting an amount of damping provided by each of said compressiondamping means and said rebound damping means.
 2. The hydraulicsuspension unit according to claim 1, wherein said passage means directsall of the flow of hydraulic liquid from said first chamber duringcompression of the suspension unit to said reservoir via saidcompression damping means and directs all of the flow of hydraulicliquid from the reservoir to the first chamber via said rebound dampingmeans.
 3. The hydraulic suspension unit according to claim 1, whereinsaid spring means includes a pressurized gas arranged in an enclosedspace in said suspension unit for acting on said movable wall of saidreservoir.
 4. The hydraulic suspension unit according to claim 3,further comprising externally accessible means for adjusting a volume ofsaid enclosed space containing said pressurized gas for adjusting aspring characteristic of said spring means.
 5. The hydraulic suspensionunit according to claim 3, wherein said spring means comprises a coilspring acting on said movable wall, said coil spring being arranged insaid enclosed space containing said pressurized gas, and externallyassessable means for adjustably preloading said coil spring.
 6. Thehydraulic suspension unit according to claim 1, wherein said rebounddamping means includes a rebound damping valve which is movable inresponse to pressure of said hydraulic liquid thereon for opening andclosing said passage means for controlling the flow of hydraulic liquidthrough said passage means from said reservoir to said first chamberduring release of stored energy from said spring means, and furthercomprising means for adjustably limiting the maximum flow area forhydraulic liquid flowing from said reservoir to said first chamber whensaid rebound damping valve is opened for controlling a maximum speed ofexpansion of said suspension unit due to release of stored energy fromsaid spring means.
 7. The hydraulic suspension unit according to claim6, wherein said means for adjustably limiting the maximum flow areaincludes a mechanical stop limiting the opening of said rebound dampingvalve, and wherein said externally accessible means adjusts the positionof said stop.
 8. The hydraulic suspension unit according to claim 1,wherein said rebound damping means includes a rebound damping valvewhich is movable in response to pressure of said hydraulic liquidthereon for opening and closing said passage means for controlling theflow of hydraulic liquid through said passage means from said reservoirto said first chamber during release of stored energy from said springmeans, and further comprising means for adjustably, resiliently biasingthe rebound damping valve in a position closing said passage means forcontrolling the hydraulic liquid pressure necessary for moving saidrebound damping valve to open said passage means permitting the flow ofhydraulic liquid from said reservoir to said first chamber and therelease of stored energy of said spring means.
 9. A hydraulic suspensionunit comprising:first and second members arranged in telescopingrelation with one another for relative movement along a longitudinalaxis of said suspension unit with changes in force on said suspensionunit compressing and extending said suspension unit within an extensionlimit of the suspension unit; means containing a hydraulic liquid, saidcontaining means including a first chamber containing hydraulic liquidin compressive force transmitting relation between said first and secondmembers without resisting extension of said suspension unit to saidextension limit by external forces on said suspension unit, the volumeof said first chamber being decreased and increased with relativemovement of said first and second members toward and away from oneanother along said longitudinal axis, respectively and said containingmeans further including a reservoir containing hydraulic liquid andpassage means connecting said first chamber and said reservoir to permitthe flow of hydraulic liquid between said first chamber and saidreservoir, said reservoir including a movable wall which can be movedback and forth to increase and decrease the volume of said reservoir asa function of the volume of the hydraulic liquid flowing to and fromsaid reservoir, respectively; spring means for resiliently biasing saidmovable wall against the hydraulic liquid in said reservoir with a forcewhich is a function of the amount of movement of said spring means andin turn the position of said movable wall and volume of said reservoir,said spring means storing energy upon movement of said movable wallincreasing the volume of said reservoir with the flow of hydraulicliquid to said reservoir, and said spring means releasing said storedenergy upon movement of said movable wall decreasing the volume of saidreservoir with the flow of hydraulic liquid from said reservoir to saidfirst chamber; compression damping means for damping the flow ofhydraulic liquid from said first chamber to said reservoir when saidsuspension unit is compressed to cause relative movement of said firstand second members towards one another alone said longitudinal axisdecreasing the volume of said first chamber; and rebound damping meansfor only affecting the rebound velocity of the initially compressedsuspension unit when such velocity is due to the force imparted by thespring means when it is returning stored energy after some initialcompression, said rebound damping means damping the flow of hydraulicliquid to said first chamber resulting from said spring means releasingenergy stored therein by moving said movable wall to decrease the volumeof said reservoir and flow hydraulic fluid from said reservoir to saidfirst chamber for extending said suspension unit, while said rebounddamping means and said suspension unit at the same time not resistingrelative movement of said first and second members away from one anotherfor extending said suspension unit to said extension limit of saidsuspension unit by external forces on said suspension unit; wherein saidrebound damping means includes a rebound damping valve which is movablein response to pressure of said hydraulic liquid thereon for opening andclosing said passage means for controlling the flow of hydraulic liquidthrough said passage means from said reservoir to said first chamberduring release of stored energy from said spring means, and furthercomprising means for adjustably, resiliently biasing the rebound dampingvalve in a position closing said passage means for controlling thehydraulic liquid pressure necessary for moving said rebound dampingvalve to open said passage means permitting the flow of hydraulic liquidfrom said reservoir to said first chamber and the release of storedenergy of said spring means, wherein said rebound damping valve is inthe form of a poppet valve, and wherein said means for adjustably,resiliently biasing includes a coil spring and externally accessiblemeans for adjusting a preload on said coil spring resiliently biasingthe poppet valve in a position closing said passage means.
 10. Thehydraulic suspension unit according to claim 1, wherein said rebounddamping means includes a rebound damping valve which is movable inresponse to pressure of said hydraulic liquid thereon for opening andclosing said passage means for controlling the flow of hydraulic fluidthrough said passage means from said reservoir to said first chamberduring release of stored energy from said spring means, and wherein thesurface areas of the upstream and downstream sides of said rebounddamping valve are relatively small and relatively large, respectively,for enhancing the opening characteristic of said valve and the returnflow of fluid from said reservoir to said first chamber when saidsuspension unit is extended by external forces.
 11. The hydraulicsuspension unit according to claim 10, wherein said ratio of surfaceareas is at least 1.5:1.
 12. The hydraulic suspension unit according toclaim 1, wherein said compression damping means includes a compressiondamping valve which is movable in response to pressure of said hydraulicliquid thereon for opening and closing said passage means forcontrolling the flow of hydraulic liquid through said passage means fromsaid first chamber to said reservoir during compression of saidsuspension unit, and further comprising means for adjustably biasing thecompression damping valve in a position closing said passage means forcontrolling the hydraulic liquid pressure and hence compressive force onthe suspension unit necessary for moving said compression damping valveto open said passage means permitting the flow of hydraulic liquid fromsaid first chamber to said reservoir and the compression of saidsuspension unit.
 13. The hydraulic suspension unit according to claim12, wherein said compression damping valve is in the form of a flexibledisk, and wherein said means for adjustably biasing applies anadjustable preload on said disk to effect the hydraulic pressurenecessary to deflect said disk and open said passage means.
 14. Thehydraulic suspension unit according to claim 1, wherein said compressiondamping means includes a compression damping valve which is movable inresponse to pressure of said hydraulic liquid thereon for opening andclosing said passage means for controlling the flow of hydraulic liquidthrough said passage means through said first chamber to said reservoirduring compression of said suspension unit, and further comprising meansfor adjustably limiting the maximum flow area for hydraulic liquidflowing from said first chamber to said reservoir when said compressiondamping valve is open for controlling a maximum speed of compression ofsaid suspension unit.
 15. The hydraulic suspension unit according toclaim 14, wherein said means for adjustably limiting the maximum flowarea includes a mechanical stop limiting the opening extent of saidcompression damping valve, and means for adjusting the position of saidstop.
 16. The hydraulic suspension unit according to claim 14, whereinsaid means for adjustably limiting the maximum flow area includes anadditional valve located in said passage means upstream of saidcompression damping valve with respect to the flow of hydraulic liquidfrom said first chamber to said reservoir, and means for adjusting theextent which said additional valve restricts the flow of hydraulicliquid in said passage means during compression of said suspension unit.17. The hydraulic suspension unit according to claim 16, wherein saidadditional valve is a needle valve.
 18. A hydraulic suspension unitcomprising:first and second members arranged in telescoping relationwith one another for relative movement along a longitudinal axis of saidsuspension unit with changes in force on said suspension unitcompressing and extending said suspension unit; means containing ahydraulic liquid, said containing means including a first chambercontaining hydraulic liquid in force transmitting relation between saidfirst and second members, the volume of said first chamber beingdecreased and increased with relative movement of said first and secondmembers toward and away from one another along said longitudinal axis,respectively, and said containing means further including a reservoircontaining hydraulic liquid and passage means connecting said firstchamber and said reservoir to permit the flow of hydraulic liquidbetween said first chamber and said reservoir, said reservoir includinga movable wall which can be moved back and forth to increase anddecrease the volume of said reservoir as a function of the volume of thehydraulic liquid flowing to and from said reservoir, respectively;spring means for resiliently biasing said movable wall against thehydraulic liquid in said reservoir with a force which is a function ofthe amount of movement of said spring means and in turn the position ofsaid movable wall and volume of said reservoir, said spring meansstoring energy upon movement of said movable wall increasing the volumeof said reservoir with the flow of hydraulic liquid to said reservoir,and said spring means releasing said stored energy upon movement of saidmovable wall decreasing the volume of said reservoir with the flow ofhydraulic liquid from said reservoir to said first chamber; compressiondamping means for damping the flow of hydraulic liquid from said firstchamber to said reservoir when said suspension unit is compressed tocause relative movement of said first and second members towards oneanother along said longitudinal axis decreasing the volume of said firstchamber; rebound damping means for damping the flow of hydraulic liquidto said first chamber resulting from said spring means releasing energystored therein by moving said movable wall to decrease the volume ofsaid reservoir and flow hydraulic fluid from said reservoir to saidfirst chamber for extending said suspension unit; wherein said movablewall is in the form of a flexible diaphragm mounted for movement withinsaid suspension unit, said reservoir being located on one side of saidflexible diaphragm and said spring means being provided on an oppositeside of said flexible diaphragm for resiliently biasing said flexiblediaphragm against hydraulic liquid in said reservoir, and wherein saidflexible diaphragm is arranged to be in a torus shape when at theextremes of its travel, a disc of a stiff material being provided at thecenter of said flexible diaphragm for locally stiffening said center ofsaid diaphragm.
 19. The hydraulic suspension unit according to claim 1,further comprising auxiliary spring means acting to cause relativemovement along said longitudinal axis along said first and secondmembers to extend said suspension unit without resistance from saidrebound damping means.
 20. A hydraulic suspension unit comprising:firstand second members arranged in telescoping relation with one another forrelative movement along a longitudinal axis of said suspension unit withchanges in force on said suspension unit compressing and extending saidsuspension unit within an extension limit of the suspension unit; meanscontaining a hydraulic liquid, said containing means including a firstchamber containing hydraulic liquid in compressive force transmittingrelation between said first and second members without resistingextension of said suspension unit to said extension limit by externalforces on said suspension unit, the volume of said first chamber beingdecreased and increased with relative movement of said first and secondmembers toward and away from one another along said longitudinal axis,respectively and said containing means further including a reservoircontaining hydraulic liquid and passage means connecting said firstchamber and said reservoir to permit the flow of hydraulic liquidbetween said first chamber and said reservoir, said reservoir includinga movable wall which can be moved back and forth to increase anddecrease the volume of said reservoir as a function of the volume of thehydraulic liquid flowing to and from said reservoir, respectively;spring means for resiliently biasing said movable wall against thehydraulic liquid in said reservoir with a force which is a function ofthe amount of movement of said spring means and in turn the position ofsaid movable wall and volume of said reservoir, said spring meansstoring energy upon movement of said movable wall increasing the volumeof said reservoir with the flow of hydraulic liquid to said reservoir,and said spring means releasing said stored energy upon movement of saidmovable wall decreasing the volume of said reservoir with the flow ofhydraulic liquid from said reservoir to said first chamber; compressiondamping means for damping the flow of hydraulic liquid from said firstchamber to said reservoir when said suspension unit is compressed tocause relative movement of said first and second members towards oneanother along said longitudinal axis decreasing the volume of said firstchamber; and rebound damping means for only affecting the reboundvelocity of the initially compressed suspension unit when such velocityis due to the force imparted by the spring means when it is returningstored energy after some initial compression, said rebound damping meansdamping the flow of hydraulic liquid to said first chamber resultingfrom said spring means releasing energy stored therein by moving saidmovable wall to decrease the volume of said reservoir and flow hydraulicfluid from said reservoir to said first chamber for extending saidsuspension unit, while said rebound damping means and said suspensionunit at the same time not resisting relative movement of said first andsecond members away from one another for extending said suspension unitto said extension limit of said suspension unit by external forces onsaid suspension unit, and further comprising auxiliary spring meansacting to cause relative movement along said longitudinal axis alongsaid first and second members to extend said suspension unit withoutresistance from said rebound damping means, and wherein said auxiliaryspring means is external to said telescoping first and second members.21. The hydraulic suspension unit according to claim 19, wherein saidauxiliary spring means is arranged inside of one of said first andsecond members.
 22. The hydraulic suspension unit according to claim 21,wherein said auxiliary spring means is located in said first chamber.23. The hydraulic suspension unit according to claim 21, wherein saidfirst chamber includes a movable wall defining a portion of said firstchamber, said auxiliary spring means yieldably biasing said movable wallof said first chamber in a direction tending to reduce the volume ofsaid first chamber.
 24. A hydraulic suspension unit comprising:first andsecond members arranged in telescoping relation with one another forrelative movement along a longitudinal axis of said suspension unit withchanges in force on said suspension unit compressing and extending saidsuspension unit within an extension limit of the suspension unit; meanscontaining a hydraulic liquid, said containing means including a firstchamber containing hydraulic liquid in compressive force transmittingrelation between said first and second members without resistingextension of said suspension unit to said extension limit by externalforces on said suspension unit, the volume of said first chamber beingdecreased and increased with relative movement of said first and secondmembers toward and away from one another along said longitudinal axis,respectively, and said containing means further including a reservoircontaining hydraulic liquid and passage means connecting said firstchamber and said reservoir to permit the flow of hydraulic liquidbetween said first chamber and said reservoir, said reservoir includinga movable wall which can be moved back and forth to increase anddecrease the volume of said reservoir as a function of the volume of thehydraulic liquid flowing to and from said reservoir, respectively;spring means for resiliently biasing said movable wall against thehydraulic liquid in said reservoir with a force which is a function ofthe amount of movement of said spring means and in turn the position ofsaid movable wall and volume of said reservoir, said spring meansstoring energy upon movement of said movable wall increasing the volumeof said reservoir with the flow of hydraulic liquid to said reservoir,and said spring means releasing said stored energy upon movement of saidmovable wall decreasing the volume of said reservoir with the flow ofhydraulic liquid from said reservoir to said first chamber; compressiondamping means for damping the flow of hydraulic liquid from said firstchamber to said reservoir when said suspension unit is compressed tocause relative movement of said first and second members towards oneanother along said longitudinal axis decreasing the volume of said firstchamber; and rebound damping means for only affecting the reboundvelocity of the initially compressed suspension unit when such velocityis due to the force imparted by the spring means when it is returningstored energy after some initial compression, said rebound damping meansdamping the flow of hydraulic liquid to said first chamber resultingfrom said spring means releasing energy stored therein by moving saidmovable wall to decrease the volume of said reservoir and flow hydraulicfluid from said reservoir to said first chamber for extending saidsuspension unit, while said rebound damping means and said suspensionunit at the same time not resisting relative movement of said first andsecond members away from one another for extending said suspension unitto said extension limit of said suspension unit by external forces onsaid suspension unit, wherein said containing means further comprises anadditional reservoir containing hydraulic liquid and additional passagemeans connecting said first chamber and said additional reservoir topermit the flow of hydraulic liquid between said first chamber and saidadditional reservoir, said additional reservoir including an additionalmovable wall which can be moved back and forth to increase and decreasethe volume of said additional reservoir as a function of the volume ofthe hydraulic liquid flowing to and from said additional reservoir,respectively, and additional spring means for resiliently biasing saidadditional movable wall against the hydraulic liquid in said additionalreservoir with a force which is a function of the amount of movement ofsaid additional spring means and in turn the position of said additionalmovable wall and volume of said additional reservoir.
 25. The hydraulicsuspension unit according to claim 24, wherein one of said movable walland said additional movable wall is a resilient bladder and the other isa piston, said spring means resiliently biasing said resilient bladderincluding a pressurized gas and said spring means resiliently biasingsaid piston including a coil spring, said suspension unit furthercomprising externally accessible means for adjusting the volume of anenclosed space containing said pressurized gas, and externallyaccessible means for adjusting a preload of said coil spring.
 26. Thehydraulic suspension unit according to claim 1, wherein said movablewall is in the form of a piston mounted for movement within a cylinderin said suspension unit, said reservoir being located on one side ofsaid piston and said spring means being provided on an opposite side ofsaid piston for resiliently biasing said piston against hydraulic liquidin said reservoir.
 27. The hydraulic suspension unit according to claim1, wherein said movable wall is in the form of an elastic bladdermounted for movement within said suspension unit, said reservoir beinglocated on one side of said elastic bladder and said spring means beingprovided on an opposite side of said elastic bladder for resilientlybiasing said bladder against hydraulic liquid in said reservoir.
 28. Thehydraulic suspension unit according to claim 1, wherein said movablewall is in the form of a flexible diaphragm mounted for movement withinsaid suspension unit, said reservoir being located on one side of saidflexible diaphragm and said spring means being provided on an oppositeside of said flexible diaphragm for resiliently biasing said flexiblediaphragm against hydraulic liquid in said reservoir.
 29. The hydraulicsuspension unit according to claim 1, wherein said rebound damping valveis arranged for movement so as to displace hydraulic liquid on the firstchamber side of the rebound damping valve during opening of said valve,the volume of said rebound damping valve and its linear travel duringopening being selected to provide displacement of a predetermined volumeof hydraulic liquid and hence a predetermined expansion of saidsuspension unit during opening of said valve.
 30. A hydraulic suspensionunit comprising:first and second members arranged in telescopingrelation with one another for relative movement along a longitudinalaxis of said suspension unit with changes in force on said suspensionunit compressing and extending said suspension unit within an extensionlimit of the suspension unit; means containing a hydraulic liquid, saidcontaining means including a first chamber containing hydraulic liquidin compressive force transmitting relation between said first and secondmembers without resisting extension of said suspension unit to saidextension limit by external forces on said suspension unit, the volumeof said first chamber being decreased and increased with relativemovement of said first and second members toward and away from oneanother along said longitudinal axis, respectively, and said containingmeans further including a reservoir containing hydraulic liquid andpassage means connecting said first chamber and said reservoir to permitthe flow of hydraulic liquid between said first chamber and saidreservoir, said reservoir including a movable wall which can be movedback and forth to increase and decrease the volume of said reservoir asa function of the volume of the hydraulic liquid flowing to and fromsaid reservoir, respectively; spring means for resiliently biasing saidmovable wall against the hydraulic liquid in said reservoir with a forcewhich is a function of the amount of movement of said spring means andin turn the position of said movable wall and volume of said reservoir,said sprint means storing energy upon movement of said movable wallincreasing the volume of said reservoir with the flow of hydraulicliquid to said reservoir, and said spring means releasing said storedenergy upon movement of said movable wall decreasing the volume of saidreservoir with the flow of hydraulic liquid from said reservoir to saidfirst chamber; compression damping means for damping the flow ofhydraulic liquid from said first chamber to said reservoir when saidsuspension unit is compressed to cause relative movement of said firstand second members towards one another along said longitudinal axisdecreasing the volume of said first chamber; and rebound damping meansfor only affecting the rebound velocity of the initially compressedsuspension unit when such velocity is due to the force imparted by thespring means when it is returning stored energy after some initialcompression, said rebound damping means damping the flow of hydraulicliquid to said first chamber resulting from said spring means releasingenergy stored therein by moving said movable wall to decrease the volumeof said reservoir and flow hydraulic fluid from said reservoir to saidfirst chamber for extending said suspension unit, while said rebounddamping means and said suspension unit at the same time not resistingrelative movement of said first and second members away from one anotherfor extending said suspension unit to said extension limit of saidsuspension unit by external forces on said suspension unit, wherein saidrebound damping means includes a rebound damping valve which is movablein response to pressure of said hydraulic liquid thereon for opening andclosing said passage means for controlling the flow of hydraulic liquidthrough said passage means from said reservoir to said first chamberduring release of stored energy from said spring means, and wherein saidrebound damping valve is arranged for movement so as to displacehydraulic liquid on the first chamber side of the rebound damping valveduring opening of said valve, the volume of said rebound damping valveand its linear travel during opening, being selected to providedisplacement of a predetermined volume of hydraulic liquid and hence apredetermined expansion of said suspension unit during opening of saidvalve; and wherein said rebound damping valve is configured to require apredetermined linear travel before allowing any flow of hydraulic liquidpast said rebound damping valve.
 31. The hydraulic suspension unitaccording to claim 1, wherein each of said compression damping means andsaid rebound damping means acts as a check valve against flow ofhydraulic liquid in the opposite direction from that which is dampedthereby.
 32. In a lightweight, wheeled vehicle where rider weight is arelatively large percentage of total sprung weight of said vehicle, saidvehicle including a vehicle body, a vehicle wheel and a hydraulicsuspension unit for supporting weight of said vehicle in relation tosaid wheel, the improvement comprising said hydraulic suspension unitcomprising:first and second members arranged in telescoping relationwith one another for relative movement along a longitudinal axis of saidsuspension unit with changes in force on said suspension unitcompressing and extending said suspension unit within an extension limitof the suspension unit; means containing a hydraulic liquid, saidcontaining means including a first chamber containing hydraulic liquidin compressive force transmitting relation between said first and secondmembers without resisting extension of said suspension unit to saidextension limit by external forces on said suspension unit, the volumeof said first chamber being decreased and increased with relativemovement of said first and second members toward and away from oneanother along said longitudinal axis, respectively, and said containingmeans further including a reservoir containing hydraulic liquid andpassage means connecting said first chamber and said reservoir to permitthe flow of hydraulic liquid between said first chamber and saidreservoir, said reservoir including a movable wall which can be movedback and forth to increase and decrease the volume of said reservoir asa function of the volume of the hydraulic liquid flowing to and fromsaid reservoir, respectively; spring means for resiliently biasing saidmovable wall against the hydraulic liquid in said reservoir with a forcewhich is a function of the amount of movement of said spring means andin turn the position of said movable wall and volume of said reservoir,said spring means storing energy upon movement of said movable wallincreasing the volume of said reservoir with the flow of hydraulicliquid to said reservoir, and said spring means releasing said storedenergy upon movement of said movable wall decreasing the volume of saidreservoir with the flow of hydraulic liquid from said reservoir to saidfirst chamber; compression damping means for damping the flow ofhydraulic liquid from said first chamber to said reservoir when saidsuspension unit is compressed to cause relative movement of said firstand second members towards one another along said longitudinal axisdecreasing the volume of said first chamber; and rebound damping meansfor only affecting the rebound velocity of the initially compressedsuspension unit when such velocity is due to the force imparted by thespring means when it is returning stored energy after some initialcompression, said rebound damping means damping the flow of hydraulicliquid to said first chamber resulting from said spring means releasingenergy stored therein by moving said movable wall to decrease the volumeof said reservoir and flow hydraulic fluid from said reservoir to saidfirst chamber for extending said suspension unit, while said rebounddamping means and said suspension unit at the same time not resistingrelative movement of said first and second members away from one anotherfor extending said suspension unit to said extension limit of thesuspension unit by external forces on said suspension unit; andexternally accessible means for independently adjusting each of a springcharacteristic of said spring means and an amount of rebound dampingprovided by said rebound damping means.
 33. The lightweight vehicleaccording to claim 32, further comprising externally accessible meansfor adjusting an amount of compression damping provided by saidcompression damping means.
 34. The lightweight vehicle according toclaim 32, wherein said passage means directs all of the flow ofhydraulic liquid from said first chamber during compression of thesuspension unit to said reservoir via said compression damping means anddirects all of the flow of hydraulic liquid from the reservoir to thefirst chamber via said rebound damping means.
 35. A hydraulic suspensionunit comprising:first and second members arranged in telescopingrelation with one another for relative movement along a longitudinalaxis of said suspension unit with changes in force on said suspensionunit compressing and extending said suspension unit within an extensionlimit of the suspension unit; means containing a hydraulic liquid, saidcontaining means including a first chamber containing hydraulic liquidin compressive force transmitting relation between said first and secondmembers without resisting extension of said suspension unit to saidextension limit by external forces on said suspension unit, the volumeof said first chamber being decreased and increased with relativemovement of said first and second members toward and away from oneanother along said longitudinal axis, respectively, and said containingmeans further including a reservoir containing hydraulic liquid andpassage means connecting said first chamber and said reservoir to permitthe flow of hydraulic liquid between said first chamber and saidreservoir, said reservoir including a movable wall which can be movedback and forth to increase and decrease the volume of said reservoir asa function of the volume of the hydraulic liquid flowing to and fromsaid reservoir, respectively; spring means for resiliently biasing saidmovable wall against the hydraulic liquid in said reservoir with a forcewhich is a function of the amount of movement of said spring means andin turn the position of said movable wall and volume of said reservoir,said spring means storing energy upon movement of said movable wallincreasing the volume of said reservoir with the flow of hydraulicliquid to said reservoir, and said spring means releasing said storedenergy upon movement of said movable wall decreasing the volume of saidreservoir with the flow of hydraulic liquid from said reservoir to saidfirst chamber; compression damping means for damping the flow ofhydraulic liquid from said first chamber to paid reservoir when saidsuspension unit is compressed to cause relative movement of said firstand second members towards one another along said longitudinal axisdecreasing the volume of said first chamber; rebound damping means foronly affecting the rebound velocity of the initially compressedsuspension unit when such velocity is due to the force imparted by thespring means when it is returning stored energy after some initialcompression, said rebound damping means damping the flow of hydraulicliquid to said first chamber resulting from said spring means releasingenergy stored therein by moving said movable wall to decrease the volumeof said reservoir and flow hydraulic fluid from said reservoir to saidfirst chamber for extending said suspension unit, while said rebounddamping means and said suspension unit at the same time not resistingrelative movement of said first and second members away from one anotherfor extending said suspension unit to said extension limit of thesuspension unit by external force on said suspension unit; wherein saidcompression damping means includes a compression damping valve which ismovable in response to pressure of said hydraulic liquid thereon foropening and closing said passage means for controlling the flow ofhydraulic liquid through said passage means from said first chamber tosaid reservoir during compression of said suspension unit, and furthercomprising means for adjustably biasing the compression damping valve ina position closing said passage means for controlling the hydraulicliquid pressure and hence compressive force on the suspension unitnecessary for moving said compression damping valve to open said passagemeans permitting the flow of hydraulic liquid from said first chamber tosaid reservoir and the compression of said suspension unit; and whereinsaid means for adjustably biasing the compression damping valve alsosimultaneously adjustably limits the maximum flow area for hydraulicliquid flowing from said first chamber to said reservoir when saidcompression damping valve is open for controlling a maximum speed ofcompression of said suspension unit.
 36. The hydraulic suspension unitaccording to claim 35, wherein said passage means directs all of theflow of hydraulic liquid from said first chamber during compression ofthe suspension unit to said reservoir via said compression damping meansand directs all of the flow of hydraulic liquid from the reservoir tothe first chamber via said rebound damping means.
 37. A hydraulicsuspension unit comprising:first and second members arranged intelescoping relation with one another for relative movement along alongitudinal axis of said suspension unit with changes in force on saidsuspension unit compressing and extending said suspension unit within anextension limit of the suspension unit; means containing a hydraulicliquid, said containing means including a first chamber containinghydraulic liquid in compressive force transmitting relation between saidfirst and second member without resisting extension of said suspensionunit to said extension limit by external forces on said suspension unit,the volume of said first chamber being decreased and increased withrelative movement of said first and second members toward and away fromone another along said longitudinal axis, respectively, and saidcontaining means further including a reservoir containing hydraulicliquid and passage means connecting said first chamber and saidreservoir to permit the flow of hydraulic liquid between said firstchamber and said reservoir, said reservoir including a movable wallwhich can be moved back and forth to increase and decrease the volume ofsaid reservoir as a function of the volume of the hydraulic liquidflowing to and from said reservoir, respectively; spring means forresiliently biasing said movable wall against the hydraulic liquid insaid reservoir with a force which is a function of the amount ofmovement of said spring means and in turn the position of said movablewall and volume of said reservoir, said spring means storing energy uponmovement of said movable wall increasing the volume of said reservoirwith the flow of hydraulic liquid to said reservoir, and said springmeans releasing said stored energy upon movement of said movable walldecreasing the volume of said reservoir with the flow of hydraulicliquid from said reservoir to said first chamber; compression dampingmeans for damping the flow of hydraulic liquid from said first chamberto said reservoir when said suspension unit is compressed to causerelative movement of said first and second members toward one anotheralong said longitudinal axis decreasing the volume of said firstchamber, said compression damping means including a compression dampingvalve which is movable in response to pressure of said hydraulic liquidthereon for opening and closing said passage means for controlling theflow of hydraulic liquid through said passage means from said firstchafer to said reservoir during compression of said suspension unit, andmeans for adjustably biasing the compression damping valve in a positionclosing said passage means for controlling the hydraulic liquid pressureand hence compressive force on the suspension unit necessary for movingsaid compression damping valve to open said passage means permitting theflow of hydraulic liquid from said first chamber to said reservoir andthe compression of said suspension unit; rebound damping means for onlyaffecting the rebound velocity of the initially compressed suspensionunit when such velocity is due to the force imparted by the spring meanswhen it is returning stored energy after some initial compression, saidrebound damping means damping the flow of hydraulic liquid to said firstchamber resulting from said spring means releasing energy stored thereinby moving said movable wall to decrease the volume of said reservoir andflow hydraulic fluid from said reservoir to said first chamber forextending said suspension unit, while said rebound damping means andsaid suspension unit at the same time not resisting relative movement ofsaid first and second members away from one another for extending saidsuspension unit to said extension limit of the suspension unit byexternal forces on said suspension unit, said rebound damping meansincluding a rebound damping valve which is movable in response topressure of said hydraulic liquid thereon for opening and closing saidpassage means for controlling the hydraulic liquid through said passagemeans from said reservoir to said first chamber during release of storedenergy from said spring means, and means for adjustably limiting themaximum flow area for hydraulic liquid flowing from said reservoir tosaid first chamber when said rebound damping valve is opened forcontrolling a maximum speed of expansion of said suspension unit due torelease of stored energy from said spring means, and means foradjustably, resiliently biasing the rebound damping valve in a positionclosing said passage means for controlling the hydraulic liquid pressurenecessary for moving said rebound damping valve to open said passagemeans permitting the flow of hydraulic liquid from said reservoir tosaid first chamber and the release of stored energy of said springmeans; and wherein said means for adjustably limiting the maximum flowarea for hydraulic liquid flowing from said first chamber to saidreservoir when said compression damping valve is open for controlling amaximum speed compression of said suspension unit includes an additionalvalve located in said passage means upstream of said compression dampingvalve with respect to the flow of hydraulic liquid from said firstchamber to said reservoir, and means for adjusting the extent which saidadditional valve restricts the flow of hydraulic liquid in said passagemeans during compression of said suspension unit.
 38. The hydraulicsuspension unit according to claim 37, wherein said compression dampingvalve and said rebound damping valve are arranged coaxially in a singleassembly in said hydraulic suspension unit.
 39. The hydraulic suspensionunit according to claim 37, wherein said passage means directs all ofthe flow of hydraulic liquid from said first chamber during compressionof the suspension unit to said reservoir via said compression dampingmeans and directs all of the flow of hydraulic liquid from the reservoirto the first chamber via said rebound damping means.